1. Field of Endeavor
The present invention relates to silica extraction and more particularly to silica extraction from geothermal water.
2. State of Technology
U.S. Pat. No. 5,200,165 for controlled precipitation of amorphous, silica from geothermal issued to Ross T. Harper et al Apr. 6, 1993 provides the following state of technology information: “amorphous silicas are differentiated by structure into three classifications; namely, TYPES I, II and III. Type I silica, defined here, is precipitated from geothermal water. This silica is commonly sourced for commercial use by acid treatment of sodium silicate solutions prepared for example, by the digestion of quartz sand with sodium hydroxide. Type II and III silicas, defined here, may be precipitated from geothermal water or an alternate aqueous source. This alternative feedstock fluid should contain sufficient initial silicic acid and or silicate ion to allow controlled precipitation as described for geothermal water in this patent. Type II precipitated silica is similar in structure to a class of commercial silicas normally prepared under anhydrous conditions, known as pyrogenic “arc” silicas. The “arc” process involves the oxidation of silicon monoxide [SiO] at very high temperatures under anhydrous conditions. Geothermal water is normally characterized as being slightly acidic to neutral to slightly alkaline with significant concentrations of SiO.sub.2, Na, K, Li, Ca, Mg, Rb, Cs, B, SO.sub.4, Cl and dissolved gaseous species, e.g. CO.sub.2, H.sub.2 S and NH.sub.3. Almost always, arsenic is present. A detailed chemical composition is shown in Table 8. Arsenic contamination of precipitated silicas from a geothermal source may or may not be a problem, depending on the end usage of the precipitated silica. Thus while in some applications procedures must be adopted whereby the arsenic contamination of silica is reduced, for others it may not be necessary. For example, where amorphous silica is being precipitated for paper coating or impregnation usage, preferably the arsenic concentration is low, e.g. less than 2 mg kg.sup.-1 in the paper sheet.”
U.S. Pat. No. 5,595,717 for controlled precipitation of amorphous silica from geothermal fluids or other aqueous media containing silicic acid issued to Ross T. Harper et al Jan. 21, 1997 provides the following state of technology information: “Moderate concentrations of silicic acid are present in hot, pressurized, aqueous, geothermal fluid as a result of the dissolution of silica containing minerals from the rock material in contact with the geothermally heated water while it is still underground. This fluid may be discharged from normal surface manifestations or may be produced artificially, from wells drilled into suitable formations, which increase mass withdrawal, for whatever purpose. Usually, the purpose of drilling geothermal wells and producing the hot geothermal fluid is to provide an energy source for the production of electric power. If silicic acid concentration in the water produced at the surface is sufficiently high, when the temperature or the pressure of the water is reduced, polymerization, with spontaneous homogeneous nucleation, of the siliceous values in the produced water results in the formation of critical size nuclei, which rapidly grow to form primary particles of silica. Spontaneous nucleation of the parent monomeric silicic acid species, and subsequent growth thereof by polymerization, forms polymeric primary silica particles which attain a physical dimension of about 1.5 nm.”